Voltammetric Determination of α-Lipoic Acid using Carbon Fiber Microelectrode in Acetic Acid – Acetonitrile Solutions

The work aimed to develop a new voltammetric method for the identification and determination of α-lipoic acid in pharmaceutical preparations. In our previous article, we proved that a mixture of acetic acid and acetonitrile (20%, v/v), containing of 0.1 M CH3COONa as a supporting electrolyte, as well as differential pulse voltammetry (DPV) on a carbon fiber microelectrode are convenient for voltammetric study of the electrochemical properties of LA. The oxidation process of α-lipoic acid, characterized as quasi-reversible and diffusion controlled, proceeds with the exchange of one electron giving unstable cation radical as primary product (EqCi mechanism). This electrode reaction was the basis for developing a new voltammetric method of LA determination with the use of both the DPV technique, and the multiple standard addition method. The proposed procedure makes it possible to determine LA without the need to separate it from the matrix and it has a wide linear range (0.25-123.2 mg L-1) and low detection limit (0.08 mg L-1). Additionally, it is accurate, precise, and can be applied for LA determination in pharmaceutical products as an alternative to widely used chromatographic methods.